Green’s Dictionary of Slang

of the penis, erect, aroused, ’ready for action’.

1967		S. Symons Place d’Armes 36: Yvon jabs his cocked pants into my thighside [Simes:DLSS].
1968		‘B. Shrader’ Gay Stud’s Trip 54: [The] huge rod [...] was powerfully cocked, and as he touched it for the first time, it jerked and throbbed in his hand [Simes:DLSS].
1971		‘B. Scharde’ Happy makes it big 96: [The penis] was some three inches long fully cocked and perhaps three-quarters of an inch thick.